This invention is related to electric starter systems for internal combustion engines.
Dual axis electric starters are known which have a solenoid aligned along a first axis and an electric cranking motor and pinion gear aligned with each other along a second axis. Single axis electric starters are also known which coaxially align a solenoid, electric cranking motor and pinion gear. Hybrid forms of these electric starters have also been shown where a solenoid and pinion gear share a common axis and a cranking motor is aligned along a separate axis.
Dual axis electric starters conventionally have a crank motor shaft supported at both ends for stability. Toward an output end of the shaft is the pinion gear and over-run clutch which are coupled so as to slide axially along the shaft together. Complimentary helical splines on the shaft and a portion of the clutch transfer rotation from the shaft to the clutch and on to the pinion gear when the clutch is engaged. The solenoid when energized causes the pinion gear to slide to a travel stop, the rectilinear motion of the solenoid being transferred to the clutch via a pivotal shift lever. The solenoid plunger also carries a moving contact intended to close a switch (via a pair of stationary contacts) for application of full power to the cranking motor when the pinion gear is fully engaged with the flywheel of the engine. This arrangement as described above requires use of longer output shafts and dead clearance space for the clutch, pinion gear and related shifted components in as much as the bulk and travel of the components dictates. Some electric starters of this type also include planetary speed reduction gears which may also add to the overall length and bulk of the starter. Additionally, tolerance stack-up of components does not readily allow for the movable contact to be net with the solenoid plunger. Rather, spring elements are conventionally utilized to allow some axial movement of the contact relative the plunger to ensure switch closure when the pinion reaches the travel stop. This arrangement may cause closure of the solenoid switch prior to the pinion gear being fully meshed with the flywheel at the travel stop leading to abrupt application of full power to the cranking motor prematurely with regard to gear meshing. The situation wherein the pinion gear crashes into the flywheel without becoming engaged therewith has been addressed by allowing the solenoid to continue its stroke by another spring arrangement between the clutch housing and pinion or between the solenoid plunger and pivotal shift lever. This arrangement is intended to allow the solenoid switch to close and apply full power to the cranking motor which rotates allowing the pinion gear to mesh with the fly wheel. Damage to gear teeth may occur with these arrangement where immediate meshing does not occur or only partial meshing occurs.
Single axis (coaxial) electric starters, such as disclosed in U.S. Pat. No. 4,923,229, have a hollow cranking motor shaft, a solenoid at the rear thereof and an over-run clutch driven thereby directly or through a planetary reduction gear mechanism. The over-run clutch imparts rotation to a clutch collar which in turn imparts rotation to a pinion shaft surrounded thereby through cooperating helical splines. The pinion shaft carries a pinion gear at the outside end. The solenoid imparts rectilinear motion to the pinion shaft to urge the shaft and pinion gear carried thereby forward through the clutch collar until it reaches a stop. The solenoid plunger is linked to the pinion shaft through the hollow cranking motor shaft via a drive rod cooperating within a hollow drive tube in telescoping arrangement. Helical springs are located between the pinion gear and pinion shaft, pinion shaft and clutch collar and within the hollow drive tube urging the drive tube and drive rod to a fully extended relationship. The solenoid plunger also carries a moving contact intended to close a switch (via a pair of stationary contacts) for application of full power to the cranking motor when the pinion gear is fully engaged with the flywheel of the engine. Here again, tolerance stack-up of components requires use of a helical spring to ensure switch closure when the pinion shaft reaches the travel stop. This arrangement suffers from the same shortfall of abrupt application of full power to the cranking motor prematurely with regard to gear meshing. The situation wherein the pinion gear crashes into the flywheel without becoming engaged therewith has been similarly addressed by virtue of the spring between the pinion gear and pinion shaft and/or the spring within the hollow drive tube. This arrangement is also intended to allow the solenoid switch to close and apply full power to the cranking motor which rotates allowing the pinion gear to mesh with the fly wheel. Damage to gear teeth may occur with these arrangement where immediate meshing does not occur or only partial meshing occurs.
Hybrid forms of these electric starters, such as disclosed in U.S. Pat. No. 4,707,616, have a solenoid and pinion gear sharing a common axis and a cranking motor is aligned along a separate axis. The cranking motor applies rotation via in-line gearing to an over-run clutch outer portion. The clutch then imparts rotation to a clutch collar which in turn imparts rotation to a pinion shaft surrounded thereby through cooperating helical splines. The pinion shaft carries a pinion gear at the outside end. The solenoid imparts rectilinear motion to the pinion shaft to urge the shaft and pinion gear carried thereby forward through the clutch collar until it reaches a stop via a drive rod therebetween. Helical springs are located between the pinion shaft and clutch collar, between the pinion shaft and drive rod and between the solenoid plunger and a plunger stop. The solenoid plunger also carries a moving contact intended to close a switch (via a pair of stationary contacts) for application of full power to the cranking motor when the pinion gear is fully engaged with the flywheel of the engine. Once again, tolerance stack-up of components requires the use of a helical spring to ensure switch closure when the pinion shaft reaches the travel stop. This arrangement suffers from the same shortfall of abrupt application of full power to the cranking motor prematurely with regard to gear meshing. The situation wherein the pinion gear crashes into the flywheel without becoming engaged therewith has been similarly addressed by allowing the solenoid to continue its stroke by virtue of the spring between the pinion shaft and drive rod. This arrangement is also intended to allow the solenoid switch to close and apply full power to the cranking motor which rotates allowing the pinion gear to mesh with the fly wheel. Damage to gear teeth may occur with these arrangement where immediate meshing does not occur or only partial meshing occurs.
It can be seen that a multiplicity of biasing springs are utilized to counter the effects of tolerance stack-up leading to a proliferation of parts. The solenoid must be powerful enough to overcome the various spring forces which may be exerted thereon directly or through drive linkages. Additionally, the solenoid and appropriate bias springs must be able to fully mesh the pinion gear with the flywheel against the frictional forces therebetween when full power rotation is applied thereto prior to full meshing. Where the solenoid plunger has voids, such as central bores, necessitated by inclusion of springs and required attachments, the pull-in strength of the solenoid is lessened thereby and must be compensated by a larger overall plunger, larger solenoid coil or combination thereof. All of this requires combinations of large plungers, large coils, high current coils and associated space, mass and cost resulting therefrom.
Typically, true location of over-run clutches is accomplished by bearings or bushings assembled into end cavities thereof, thereby adding to clutch width and consuming axial space along the clutch collar upon which they bear. True location is desirable for minimal slop during over-run when the clutch is not driveably engaged to the clutch collar yet slidably rotates thereabout. To a great degree, the slop is dependent upon the individual tolerances and assembly of each part of the assembly (i.e. clutch collar, bearing/bushing, clutch cavities) thus requiring burdensome dimensional control.
Helical splines as described are utilized to assist full meshing when full power is applied to the cranking motor. They are shaped so as to urge the pinion gear forward when radially loaded by the cranking motor. Helical splines introduces complexity into the manufacturing process and are therefore desirably avoided.
U.S. Pat. Nos. 4,551,630 and 4,755,689, both assigned to the assignee of the present invention, show electric starters intended to energize the cranking motor at less than full speed prior to pinion gear and flywheel meshing to avoid certain of the outlined shortfalls occasioned by premature full power application. However, any of the electric starters described above may still be prone to full power application prior to full meshing due to the inherent tolerance stack-up of the components as described.